LED flasher does not work need help.

JonSea said:

Geez oh grief. Are you so humorless you can't recognize a joke???????

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I recognize jokes just fine. When you tell one, I'll laugh. I'll even click the now-defunct "funny" button.

I built 9 of these LED flashers today. I cut circuit boards into 4 pieces on band saw then assembled them factory assembly line style. I solder 2 transistors to each board first, then 2 capacitors, then the cross over wires, then 4 resistors, then the LEDs. I taped 2 AA batteries together then attached them to the PC boards. I ran out of 470 ohm resistors from my 470 ohm resistor package. I have a bargain package of scrambled resistor there is probably some 470s in there but that will have to wait until later. If anyone comes around after dark lights are easy to see I hope it freaks people out and they leave.

**broken link removed**

Lazy people were taking the shopping carts home. A shopping cart has a lot of expensive metal in it so thieves were taking them to the metal dump and getting paid for the metal. Then the shopping carts were fitted with a brake that stops one wheel when it passes a perimeter wire in the ground around the store. But smart crooks found it easy to tip the cart over the wire so it is not detected and braked then the stores added a looney depositer in each cart.
I collect the looneys when stupid people forget to take their refund.

JonSea said:

Maybe instead of dozens of randomly flashing LEDs, Gary should address the problem more actively.

These cheap microwave radar sensor modules could be used to switch on an LED when a person is detected. These modules have a wide, non-directional detection range, and are designed to stay on for a minute or two when motion is detected.

They operate from 4.5 volts, with a quiescent current of 3mA, with an output that will provide up to 100mA at 3-point-something volts which will be adequate for a red LED (current limiting resistor required). This is probably the most practical solution in this monumental thread and actually addresses the problem it's meant to solve.

I've played with these modules. They will detect a person through a sheetrock wall with no problem. I did a few tests to see if I could limit the field of detection without any luck. Even in a tall narrow steel can with one end open, detection was omnidirectional.

Note the price shown is for 5 boards. They are less than a buck a piece.

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Can these be used like a motion detector to turn on an LED flashlight?

Yes, the microwave radar detectors can be used like an IR detector.

As I stated, the module can supply about 3.3v @ 100mA. If this won't power whatever LEDs you want to use, you could use the output to control a transistor or FET switch.

JonSea said:

Yes, the microwave radar detectors can be used like an IR detector.

As I stated, the module can supply about 3.3v @ 100mA. If this won't power whatever LEDs you want to use, you could use the output to control a transistor or FET switch.

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I have several Harbor Freight free flashlights with bad switches. There are 11 LEDs in a flashlight it runs on 3 AAA batteries. 3 batteries is 4.5v about 1a.

I seriously doubt your flashlight is drawing an amp. At any rate, my previous comment stands.

JonSea said:

I seriously doubt your flashlight is drawing an amp. At any rate, my previous comment stands.

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Batteries are 1a but not the 11 LED lights. Online datasheet says 20ma for white LED = .02 x 11 = .22a that should work.

gary350 said:

Batteries are 1a but not the 11 LED lights. Online datasheet says 20ma for white LED = .02 x 11 = .22a that should work.

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Last time I checked, 20mA × 11 > 100mA. Verify the current draw of the flashlight before connecting it to the module output that can supply a maximum of 100mA.

My calculator says, .02 x 11 = .22 maybe that is maximum and not what it really is when the lights r ON.

0.02 AMP × 11 = 0.22 AMP

20mA × 11 = 220mA

Measure the current draw because you are just guessing what each LED may be drawing. If it's more than 100mA total, bye bye magic smoke.

Name-Brand AAA alkaline batteries can produce 1A for only a few minutes with the LEDs dimming during the discharge. The capacity is rated at 1Ah when the current is only 50mA.

Today I made 4 more circuit board so I can make 4 more LED flashers. I laid out all my used parts and tested them to make sure they are good. I did not test the NEW transistors that I bought from some place in the USA that arrived very fast. I did assembly line assembly again. I put 2 transistors on each PC board then 2 capacitors, then the cross over wires. I only have enough resistors to complete 2 boards. I soldered on the LEDs, attached the batteries and they don't work. One board 1 LED is on all the time it does not blink. The other board both LEDs are on all the time they don't blink. I double checked the circuit and connections nothing is wrong. I think I need to start testing brand new transistors to make sure they work. I tried different batteries, also tried 3 batteries instead of 2 the LEDs got brighter. Tonight I need to order more resistors. Tomorrow I need to test NEW transistors to make sure they GOOD.

You can test the transistors in the circuit. When a transistor is turned on by its 47k resistor on its base to +3V then the capacitor turns it off.
make the test by simply shorting the base to 0V and it should turn off.

I tested both transistors and caps on the PC board they test good. Double checked wires they are good. With battery connect both LED stay ON. I replaced both caps. I replaced both transistors. Both LED lights stay ON. I tried 3v and 4.5v LEDs get brighter. Both transistors have to be on for LEDs to stay on. I swapped LEDs 3 times they are both still ON.

I built 9 LED flashers they all work perfect now I have 2 that will not work. The other one has 1 LED that stays ON.

I removed parts from 1 duel LED flasher to build a single LED it works perfect. The single flasher will flash so fast it is like a photographic flash bulb. ON time is about 10% of the total flash cycle. Single flasher uses a 10uf cap the duel flasher uses 100uf caps. I am guessing there is 90% less charge in a 10uf compared to a 100uf cap. Single flasher is no good flash needs to stay on longer like the duel flasher if your not stearing right at it your not sure if saw a flash or what.?

Gary certainly has a unique troubleshooting logic.

JonSea said:

Gary certainly has a unique troubleshooting logic.

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I am out of 47k resistors & out of 470 ohm resistors too. I wanted to build 2 more flashers before dark and I wanted single LED flashers. Now I have learned 1 LED flasher is not so good. Today I experiment with changing 10uf capacitor to 100 uf to see if LED flashes brighter. I have 47K & 470 resistors on order they should be here Friday. I have trouble testing LEDs they are not all the same voltage. No problem with Red LEDs, sometimes Green will flash & sometimes not, Yellow, blue, white will not flash on 2 AA batteries.

This has been hacked to death, so I'm hesitant to add more to the discussion.

The forward voltage of an LED depends on the chemistry used to make it. Different chemistries result in different colors. So different colors of LEDs have different forward voltages, called Vf. The voltage applied must be greater than Vf for the LED to illuminate. This table is a simplified example of Vf vs color.



It's really even more complex than the table above shows. For example, green LEDs can have a number of different chemistries, so Vf varies over a wide range depending on the chemistry.

Vf for green LEDs can vary from 2.0 - 2.3 volts for most types, but can be 3.5 volts for some types.

Vf for red LEDs range from 1.7 - 2.5 volts. Almost every type of red LED will work from 2 alkaline batteries.

For an LED to illuminate in Gary's circuit, the battery voltage must be greater than the LED's Vf + the voltage drop across the transistor which can be as much as a volt. With a 2 battery supply, any LED with Vf greater than around 2 volts is pretty marginal.



Gary's efforts would be a lot easier if he understood the circuit. The current through the LED and its brightness depend on the transistor and LED series resistor. The capacitor has nothing to do with LED brightness. Increase the capacitance, and the LED will flash slower, not brighter.

Gary, I will ask again.
On your two-LEDs circuits that have one LED or two LEDs turn on all the time, did you test the transistor by shorting its base to 0V for it to turn off the LED?

The capacitor on the single LED flasher charges slowly when the transistors and LED are turned off, then the transistors and LED discharge the capacitor quickly causing a short flash duration.
The two-LEDs flasher circuit simple lights one LED then lights the other LED so that each LED is on for the same amount of time that it is off.

We had to do real life stuff today but I did get to experiment a little.

I used the 1 LED flasher to test capacitors and LEDs. I put a 100uf cap in parallel with the 10uf cap flash time changed from 1 second to about 10 seconds. I removed the 100uf caps from the dual LED flasher and tested them with my LCR meter, they all test near 87uf to 91uf. I decided to put the caps in parallel with the 10uf on the 1 LED flasher to see if they really do work. 2 of these caps will not work on the 1 LED flasher. I trashed the 2 bad capacitors. It seems like if capacitor is bad LCR meter would not read it value.

Next I removed LEDs from the flasher circuits and test them along with others I had tried to use and left laying on the work bench. When I put a red LED in parallel with a flashing red LED they both blink. ALL the green LEDs look identical but some will not blink when in parallel with the blinking red LED. None of the, blue, yellow, white LEDs will blink in parallel with the blinking Red LED. It looks like all the green LEDs are not the same or some are bad or some need higher voltage.

When I built this circuit LED flashed too fast so i changed 1uf to 10uf it flashes about 2 times per second. Then I reduced 1M to 470K now it blinks 1 time per second. LED flashes so quick it does not appear to be coming ON all the way to full brightness so I changed 10uf to 30uf. Now LED is lighting up much brighter blinking 1 time in 3 seconds.

I know this as a very simple circuit but it has been a educational learning experience.

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